1. Field of the Invention
The present invention is related to an exposure apparatus for an optical disc. More particular, the present invention is related to an exposure apparatus having vibration means capable of vibrating to eliminate vibrations along the propagating direction as a rotation mechanism rotates, thereby pitches between two adjacent tracks on the optical disc can be exposed with a high precision. In addition, the present invention is related to an the exposure apparatus that a three-dimensional shape measuring device can be used for its propagation device.
2. Description of the Prior Art
Nowadays, information or data can be reproduced optically, and an optical disc is well developed for reproducing data from or recording data into the optical disc in an optical manner. The optical disc, for example, can be a compact disc (CD), a compact disc-read only memory (CD-ROM), a compact disc recordable (CD-R), or compact disc rewritable (CD-RW), etc.
In general, an exposure to the optical disc can be done by an exposure apparatus disclosed by Japanese Laid Open 10-293928, for example. The exposure apparatus includes a head fixed on the exposure apparatus through a tiny sliding device for emitting optical beams, and a sliding stage on which a turntable for supporting the optical disc is mounted. The sliding stage can be moved along a radial direction of the turntable by the sliding device installed on the exposure apparatus. The movement of the sliding stage is conducted by the tiny sliding device to compensate the position of the optical head, by which a pitch between adjacent tracks can be exposed with a highly accuracy.
Also, conventionally, in order to achieve that the track pitches with a high precision are formed on the optical disc, a laser interferometer or a laser holo-scale having a high resolution is installed on a slider propagating device that is used for mounting the recording head in a mastering device. By which, a slider propagating deviation of the mastering device is detected, and the propagating deviation is optically corrected by deviating the laser beams using an audio optical deviation device. In addition, the propagating slider and the recording head are integrated by a piezo-actuator. Using the retractable piezo-actuator to let the recording head operate, the tiny propagating deviation of the propagating slider is corrected. (see Japanese Laid Open 10-261245).
Moreover, using the exposure system assembled on the slider, laser beams for exposure are focused by an objective lens. A piezoelectric element of the objective lens for fine-tuning positions of a first tremor table is installed on a second tremor table. The optical disc and the turntable for rotating the optical disc are placed on a position opposite to the objective lens. Accordingly, by moving the first tremor table opposite to the vibration direction with the same distance as the vibration of the slider, and then the vibration of the slider is cancelled (see Japanese Laid Open 8-329476).
Additionally, during the rotation of the turntable, among phenomena that turntable vibrates in its (or the optical disc) radial direction, a technology is provided to avoid the influence on the track pitch due to irregular non-synchronized vibration that is irrelevant to the position of a rotation angle of the turntable. In regard to the exposure apparatus for recording desired information on the optical disc by irradiating laser beams thereon, the exposure apparatus comprises a non-synchronized vibration calculating device for calculating the non-synchronized vibration acted along the radial direction of the turntable, and an adjusting device for adjusting the irradiating positions of the laser beams irradiated on the optical disc according to signals from the non-synchronized vibration calculating device (see Japanese Laid Open 9-190651).
Namely, according to the exposure apparatus mentioned above, in a non-contact way a displacement sensor is placed in the radial direction of the turn table. An origin pulse signal of the turntable is triggered and each rotation position of the turntable is measured previously. And an average value by averaging each vibration amount of the angular position of the rotation is memorized and acuminated. The vibration amount measured during the exposure is subtracted by the average value corresponding to each angular position of the rotation, and then only the amount of the non-synchronized vibration is outputted for correcting the irradiating positions of the laser beams using the adjusting device. In the situation, because the exposure apparatus is able to output the non-synchronized vibration irrelevant to each angular position of the rotation of the turntable, and even though in the exposure process the accuracy of the track pitch is exerted serious problem, the non-synchronized vibration can be immediately detected during the exposure process. The exposure process, therefore, can be terminated. Furthermore, it provides a propagation mechanism that is not affected by the non-synchronized vibration of the turntable.
Therefore, according to the conventional exposure apparatus mentioned above, many improvements are required for exposing the track pitch between adjacent tracks on the optical disc with a high-precision accuracy.
Namely, according to the exposure apparatus disclosed in the Japanese Laid Open 10-293928, the head for irradiating laser beams is fixed on the main body of the exposure apparatus through a tiny sliding device, and the moving stage for installing the turntable used for supporting the optical disc is moved along the direction of the turntable by tiny sliding device fixed on the main body. With respect to the moving position of the moving stage, the position of the head for irradiating laser beams is corrected by the tiny sliding device. Therefore, the track pitches between adjacent tracks are exposed with a high-precision accuracy.
However, because the optical disc is usually placed on the turntable with an eccentricity of several ten μm with respect to the outer radius, the rotation mechanism generates rotational vibration due to the centrifugal force during rotation. Therefore, the irradiation position of the laser beam at side of the turntable varies with the rotation angle, thereby it cannot calculate the correct difference in the propagating direction. As a result, it cannot perform an accurate correction because the tiny sliding device is moved according to the incorrect measured signal. In contrast, track pitches are changed and the exposure quality becomes worse.
In addition, according to the processing method for the optical disc disclosed in the Japanese Laid Open 10-261245, the laser interferometer or the laser holo-scale are assembled for detecting a small propagating deviation of the slider, thereby the small propagating deviation of the slider is optically corrected by deviating the laser beams using an audio optical deviation device. Namely, the laser interferometer or the laser holo-scale is assembled for detecting small propagating deviation of the slider. In addition, the propagating slider and the recording head are integrated by a piezo-actuator. Using the retractable piezo-actuator to let the recording head operate, the tiny propagating deviation of the propagating slider is corrected.
However, because the pitch accuracy formed on the optical disc is determined by the relative vibration between the turntable and the moving stage, it is worse for the correction accuracy to perform the propagating correction by only using the detected result of the slider. As a result, the exposure quality cannot be increased and enhanced.
Next, according to according to disclosure in the Japanese Laid Open 8-329476, in order to eliminate the tiny vibration of the slider according to insufficient propagating servo gain due to that the small vibration of the slider driven by friction and the mechanical resonant frequency of the propagating device are low, a piezoelectric element of the objective lens for fine-tuning positions of a first tremor table is installed on a second tremor table. Accordingly, by moving the first tremor table opposite to the vibration direction with the same distance as the vibration of the slider, and then the vibration of the slider is cancelled.
However, as same as the method in the Japanese Laid Open 10-261245, it is worse for the correction accuracy to perform the propagating correction by only using the detected result of the slider. As a result, the exposure quality cannot be increased and enhanced.
In addition, according to the disclosures in the Japanese Laid Open 10-293928, Japanese Laid Open 10-261245, and Japanese Laid Open 8-329476, because the piezoactuator used as the correction mechanism for the propagating direction is installed on the fore-end or frame of the optical head, the structure is complex and its assembly is very difficult. In addition, the mechanical rigidity is reduced, and the servo gain of the propagating device cannot be set high, which inconvenient control occurs.